The invention relates to an arrayed waveguide grating, which is widely used as a key device for constructing a wavelength division multiplexed (WDM, hereinafter ) optical communication system, and multiplexes or demultiplexes WDM optical signals in accordance with wavelengths of individual optical signals.
Hitherto, an arrayed waveguide grating for multiplexing or demultiplexing WDM optical signals is well known to all as a key device for constructing the WDM optical transmission system, such as an optical wave address network or an optical switching system.
FIG. 1 is a perspective view for showing a method for controlling temperature of a conventional arrayed waveguide grating, and a reference numeral 1 shows the arrayed waveguide grating, 2 shows a metallic plate, 3 shows a temperature-control unit, 4 shows a heat sink, 5, 6 show optical fiber arrays, 7 shows an optical fiber, and 8 shows a taped optical fiber.
In the arrayed waveguide grating 1, an input waveguide 12, an input slab waveguide 13, arrayed waveguides 14 composed of plural waveguides successively extending in a length by xcex94L, an output slab waveguide 15 and N output waveguides 16 are formed on a waveguide substrate 11. The arrayed waveguide grating 1 has the function of demultiplexing the WDM optical signals, which are composed of N optical signals having the wavelength of xcex1, xcex2, . . . , xcexn and supplied through the input waveguide 12, into the N individual optical signals and outputting them through the output waveguides 16 respectively corresponding to their wavelengths.
The temperature-control unit 3 is formed of Peltier or a thin heater.
An outline of the principle of the operation of the arrayed waveguide grating 1 will be explained for a case that this circuit is used as a demultiplexer as an example.
The WDM optical signals incident on the input waveguide 12 are diffracted by the input slab waveguide 13, divided among the arrayed waveguides 14, and propagate therethrough. Although each optical signal is in the same phase in the input end of the arrayed waveguides 14, since the arrayed waveguides 14 successively extend in a length by xcex94L, each optical signal undergoes a difference in a phase between the adjacent waveguides at the output end of the arrayed waveguides 14 depending on the wavelength thereof. When each optical signal is supplied to the output slab waveguide 15 from the arrayed waveguides 14 and propagates therethrough, each optical signal is focused on one of the output waveguides 16 at the output end of the output slab waveguide 15 depending on the wavelength thereof. The WDM optical signals are demultiplexed into the N individual optical signals in this way, and outputted through the output waveguides 16.
In the arrayed waveguide grating 1, an insertion loss of the optical signal supplied to one of the output waveguides 16 becomes the minimum at a certain center wavelength. In order to make the certain center wavelength coincide with a desired wavelength, it is necessary to control the phase difference of the optical signal between the adjacent waveguides at the output end of the arrayed waveguides 14 so as to coincide with a predetermined-value.
A main ingredient of the core of the waveguide through which the optical signal propagates is SiO2 in most cases, and a refractive index of SiO2 changes in accordance with temperature. Accordingly, it is necessary to control temperature of the arrayed waveguides 14 so as to maintain a predetermined value.
In the conventional arrayed waveguide grating 1, the temperature-control unit 3 for maintaining temperature of the arrayed waveguides 14 at a predetermined value is brought into contact with a reverse surface of the waveguide substrate 11 via the metallic plate 2 in order to make the center wavelength coincide with the desired wavelength.
A thin heater or Peltier is selected as the temperature-control unit 3 in accordance with operating temperature of the arrayed waveguides 14. Generally speaking, in case that an optical circuit is so designed that the center wavelength coincides with the desired wavelength at about 80xc2x0 C., which is higher than ordinary ambient temperature, the thin heater is adopted. In case that the optical circuit is so designed that the center wavelength coincides with the desired wavelength at a medium value of ordinary ambient temperature, Peltier is adopted.
In the aforementioned conventional arrayed waveguide grating 1, since the temperature-control unit 3 for maintaining temperature thereof at a predetermined value is brought into contact with the reverse surface of the circuit substrate 11 via the metallic plate 2 and thereby temperature of the arrayed waveguides 14 is kept to be a predetermined value, the temperature-control unit 3 formed into an independent component is indispensable. As a result, since it becomes necessary to join plural parts together to fabricate the arrayed waveguide grating 1 (a module, hereinafter at need), the module cannot be thinned, and is not resistant to vibration or shock. Accordingly, fabrication process becomes complicated, and cost of production increases.
Accordingly, it is an object of the invention to provide an arrayed waveguide grating which does not necessitate a thin heater or Peltier to be combined with a module as an independent component, and has a thin, simplified and unified structure.
According to the feature of the invention, an arrayed waveguide grating comprises:
at least one input waveguide formed on a substrate,
an input slab waveguide formed on the substrate,
arrayed waveguides formed on the substrate,
an output slab waveguide formed on the substrate,
plural output waveguides formed on the substrate, and,
temperature-control means integrated with the arrayed waveguide grating
In the arrayed waveguide grating according to claim 2, the temperature-control means is formed on the arrayed waveguides.
In the arrayed waveguide grating according to claim 3, the temperature-control means is a thin film heater.
In the arrayed waveguide grating according to claim 4, the thin film heater is formed by means of evaporation.
In the arrayed waveguide grating according to claim 5, the thin film heater is formed of metal.
In the arrayed waveguide grating according to claim 6, the thin film heater is covered with a protective layer.